1. Field of the Invention
This invention relates to an apparatus and process for storage and supply of electrical energy utilizing an electrically rechargeable reduction-oxidation electrochemical cell using an anionically active species. The electrical storage and supply system of this invention provides ambient temperature operation, and storage capacity independent of both electrode size and peak instantaneous discharge rates. Energy storage is achieved exterior to the electrochemical cell which is operable by a reversible reduction-oxidation flowing electrolyte. The system may be used to store quantities of electrical energy which may be randomly produced such as by wind or optical energy and provide a stable storage and supply system capable of repeated electrical discharging and charging cycles.
2. Description of the Prior Art
Rechargeable secondary batteries with at least one reactive electrode and utilizing a bromide or iodide ion reaction are known by U.S. Pat. No. 3,214,296, while secondary batteries having a least one reactive electrode utilizing a sulfide ion-sulfide composition reaction are shown by U.S. Pat. No. 4,002,807. In each of these cases, the secondary battery is totally self-contained and is limited both in its storage capacity and in its supply capacity to the size of the active electrode region. Circulating electrolytes have been suggested for rechargeable secondary storage batteries of the zinc-halogen type wherein the halogen is stored in a corresponding solid hydrate form as exemplified by U.S. Pat. Nos. 4,105,829 and 4,181,777. However, each of these patents points out the difficulties encountered with electrical and electrode instability.
Electrically regenerable secondary batteries are taught by U.S. Pat. Nos. 3,996,064 and 4,133,941 which teach cationic active reduction-oxidation electrical storage and supply systems with flowing electrolytes. Both of these patents teach chloride ion transfer between a catholyte and anolyte through a permeable membrane and both teach the desirability of strong acid electrolytes. The 3,996,064 patent teaches a single electron transfer system limiting the cationic storage energy capacity.
Reduction-oxidation systems are known utilizing Br.sup.- /Br.sub.2, I.sup.- /I.sub.2 and S.sup.-2 /S.sub.n.sup.-2 are known in the art as exemplified by U.S. Pat. No. 4,215,182. U.S. Pat. No. 4,215,182, however, teaches utilization of a photoelectrochemical membrane cell to regenerate the redox anolyte of a redox-oxygen cell.
A variety reduction-oxidation batteries have been proposed in recent years, as exemplified by the publications: Thaller, L. H., "Recent Advances in Redox Flow Cell Storage Systems". Paper No. NASA TM-79186 presented at the Intersociety Energy Conversion Engineering Conference, Boston, August 5-10, 1979; Giner, J., Swette, L., and Cahill, K., "Screening of Redox Couples and Electrode Material", Final Report GR134705 under NASA-Lewis Contract No. NAS3-19760. Waltham, Mass.: Giner, Inc., 1976; and Hodes et al "Electrocatalytic Electrodes for the Polysulfide Redox System", J. Electrochemical Soc. 127, 544, 1980 (March). However, the proposed redox batteries have not been as satisfactory as desired: their volumetric storage capacity being relatively low, generally less than 1 mole of electrons per liter of stored electrolyte; parasitic side reactions, such as hydrogen evolution during charging; and requiring expensive and strategically important materials not readily available in this country.